1. Field of the Invention
This invention relates to a power source apparatus that powers a motor to drive an electric vehicle such as a hybrid car or electric automobile, and relates to a car power source apparatus having a simple circuit structure that can detect an open circuit in a voltage detection line for detecting battery module voltage.
2. Description of the Related Art
A power source apparatus that powers an electric vehicle detects battery voltage and controls charging and discharging to prevent over-charging and over-discharging of the driving battery. This is because over-charging and over-discharging degrade battery electrical characteristics and shorten battery lifetime. A car power source apparatus has been developed (Japanese Patent Application Disclosure 2006-25501) to prevent battery over-charging and over-discharging by detecting driving battery voltage and controlling battery charging and discharging.
The car power source apparatus cited in disclosure 2006-25501 detects voltage via a voltage detection circuit on the battery-side and on the output-side of contactors connected to the output-side of the driving battery. The car power source apparatus detects contactor voltage on the battery-side and on the output-side to determine if a contactor has fused closed. Contactors are controlled by a control circuit. When the car is driven, a main switch, which is the ignition switch, is on and contactors are switched to the off state when the ignition switch is turned off. Contactors are switched on by the control circuit when the ignition switch is turned on; namely, when car is driven. A contactor that has fused closed does not switch to the off state even if the control circuit switches it off. Therefore, when the control circuit controls the contactors off, a fused contactor can be detected by measuring voltages at the output-sides of the contactors.
It is a requirement that the voltage detection circuit reliably detect driving battery voltage when the contactors are switched on and the car is being driven. This is because the condition of the driving battery cannot be determined if driving battery voltage cannot be detected. To detect driving battery voltage, the input-side of the voltage detection circuit is connected to driving battery voltage detection nodes via voltage detection lines. If a voltage detection line becomes open circuited, voltage detection node voltage is not input to the voltage detection circuit, and driving battery voltage cannot be detected. If voltage cannot be detected, the control circuit switches the contactors off. In this state, the driving battery cannot drive the car even if the condition of the driving battery is normal. The detrimental result that voltage cannot be detected if a voltage detection line is open circuited can be resolved by connecting the input-side of the voltage detection circuit to voltage detection nodes in the driving battery via a plurality of voltage detection lines. In a car power source apparatus with this circuit structure, it is important to determine if each voltage detection line is properly connected during the manufacturing process. This is because if any voltage detection line is open circuited at the time of manufacture, the car will not be able to be driven if remaining line(s) become open circuited when operated by the user.
A car power source apparatus provided with a plurality of voltage detection lines can make decisions by detecting the voltage on each voltage detection line via the voltage detection circuit. This is because no voltage is measured by the voltage detection circuit on an open circuited voltage detection line. However, to detect voltage at one voltage detection node in the driving battery with this circuit structure, it is necessary to detect voltage at a plurality of points corresponding to the number of voltage detection lines. This results in a complex circuit structure. For example, in an apparatus that detects driving battery voltage via two voltage detection lines, voltage must be detected at twice as many voltage detection points.
The present invention was developed with the object of further resolving these drawbacks Thus it is an object of the present invention to provide a car power source apparatus that can detect voltage detection line open circuit, and determine if it impedes voltage detection. Furthermore, this is done with an extremely simple circuit structure by detecting open circuit for a plurality of voltage detection lines while measuring one voltage.